The present invention relates generally to data communication systems and devices, and more particularly to modem relay systems and other data communication applications involving multiplemodem connections.
FIG. 1 shows an example of a conventional data communication system 10 which includes a first computer 12 and a second computer 14. The first and second computers 12, 14 communicate with one another over a two-modem connection which in this example includes: a first modem 15 associated with the first computer 12; a transport medium 16; and a second modem 17 associated with the second computer 14. The transport medium 16 may include, e.g., one or more telephone lines or other communication lines associated with a Public Switched Telephone Network (PSTN), a Private Branch Exchange (PBX), a telephone line simulator (TLS), leased lines, or a portion or combination of these and other wired or wireless systems and devices. The modems 15, 17 in this conventional arrangement allow the computers 12, 14 to exchange information over the transport medium 16. As is typical, the arrangement shown in this example includes only two modems, each associated with one of the computers on a given end of the connection.
The V.24 Series Recommendation of the International Telecommunications Union-Telecommunication (ITU-T) Standardization Sector defines the signals communicated between Data Circuit Terminating Equipment (DCE) and Data Terminal Equipment (DTE) in systems such as that shown in FIG. 1. For example, in the system 10, both of the modems 15, 17 are each considered DCE, while the computers 12, 14 are each considered DTE. In accordance with the V.24. Recommendation, upon establishment of a connection capable of passing DTE-to-DTE user data, the DCE are considered to be on-line and in data mode. When off-line, or not-connected to other DCE, the DCE are said to be in command mode. A third condition can exist whereby the two endpoint DCE are on-line and in data mode, but one of the DTE has requested its near-end DCE to enter an on-line command mode. This third condition, commonly referred to as xe2x80x9cescape to on-line command mode,xe2x80x9d allows the requesting DTE to issue post-connect commands to its near-end DCE. Such commands may be used, e.g., to reconfigure the DCE, to request that the DCE disconnect, or to request that the DCE reenter on-line data mode.
After completion of data transmission through the system, the DTE on each end of the connection instructs its corresponding DCE to initiate a line disconnect sequence to electronically disengage itself from the communication line.
The data communications industry has adopted two methods of invoking a DTE-to-DCE line disconnect sequence. The first is via a hardware signaling mechanism described in ITU-T V.24 Series 108/2, and the second is by sending an escape to on-line command mode character sequence, followed by a command to disconnect the DCE from the communication line.
An end user or a suitable mechanism associated therewith, such as a DTE application program, an operating system, a Basic Input Output System (BIOS), or other software element, may initiate the escape to on-line command mode and the DTE-to-DCE line disconnect sequence. More specifically, a certain known sequence of characters, e.g., three consecutive plus characters (xe2x80x9c+++xe2x80x9d) appropriately timed, may be issued in order to force a modem or other DCE to enter on-line command mode while the DCE is in a data mode. As previously noted, the on-line command mode feature allows post-connect or data mode DCE reconfirmation. The DTE-to-DCE line disconnect is similarly generated by issuing three consecutive plus characters (xe2x80x9c+++xe2x80x9d) followed by an ATH command. For example, the dial-up networking feature of the Microsoft Windows(trademark) operating system is known to issue three plus characters (xe2x80x9c+++xe2x80x9d) followed by an ATH command in order to instruct the DCE to disconnect from the communication line.
The above-described conventional techniques can cause significant problems in certain communication systems, such as modem relay systems, that incorporate a series arrangement or chain of more than two DCE in a given DTE-to-DTE connection. More particularly, issuing the escape to on-line command mode sequence for one of the DCE in the chain may cause the other DCE in the chain to also enter on-line mode. This is undesirable because the DCE initiating the escape to on-line command mode will then have no way to instruct other DCE further down the chain with regard to subsequent commands or configuration settings, such as returning to a data mode, or terminating a connection. Such a situation can lead the system to become disjoint, with some DCE in on-line command mode and others in data mode, resulting in complications such as network equipment availability issues, potential under-billing or over-billing of communications, and fraudulent communications.
One possible solution to this problem is to disable the escape to on-line command mode entirely, for all of the DCE in the chain. However, this solution is inadequate in that it would prevent any of the DCE in the chain from obtaining the substantial benefits generally associated with that mode.
A need therefore exists for techniques for handling the above-described escape to on-line command mode in a manner that avoids the problems which can occur in connections involving chains of more than two modems or other DCE, without requiring that the mode be disabled for all the DCE in the chain.
The invention provides improved techniques for handling escape to on-line command mode in multiple-modem connections.
In accordance with the invention, a modem relay connection or other type of connection established between terminals of a communication system includes a series arrangement of multiple modems or other data communication devices. The connection includes two endpoint data communication devices, and at least one non-endpoint data communication device within the serial arrangement between the two endpoint devices. Each of the endpoint data communication devices has a first type of escape to on-line command mode feature, and the one or more non-endpoint data communication devices are each configured so as to have a second type of escape to on-line command mode feature different than the first type of escape to on-line command mode feature. This ensures that entry of the on-line command mode by one of the endpoint devices will not inadvertently disrupt the desired operation of the one or more non-endpoint devices.
The non-endpoint device may be configured to have the escape to on-line command mode feature of the second type by altering a command structure of the non-endpoint device. In one possible implementation, a register setting which is associated with the non-endpoint data communication device and utilized to implement the escape to on-line command mode feature may be changed from a default value associated with the escape to on-line command mode feature of the first type to a different value associated with the escape to on-line command mode of the second type.
As another example, the non-endpoint device may be configured to have the escape to on-line command mode feature of the second type by appropriate modification of software which detects an escape sequence. More particularly, the software may be altered by forcing a detection routine of the escape to on-line command mode to return a specified value associated with non-detection of an escape sequence.